The present invention relates to a method and apparatus for detecting the unbalanced state of a rotating shaft and a method for detecting the clamping state of a workpiece and, particularly, to a method and apparatus for quantitatively detecting the unbalanced state of a rotating shaft driven by a motor and a method for detecting the clamping state of a workpiece.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
With the technological developments, modern manufacturing and machining processes have increasingly higher and higher requirements with regard to manufacturing accuracy and precision.
However, a rotating shaft driven by a motor of manufacturing equipment (such as a machine tool) can appear in an unbalanced state for a variety of reasons, and this affects not only the service life of various mechanical components, but also the machining accuracy and precision:
the centrifugal force produced by the unbalanced state of the rotating shaft affects a smooth rotation;
the unbalanced state of the rotating shaft is a main reason resulting in the generation of vibration;
the vibration due to the unbalanced state of the rotating shaft will cause the workpiece to jitter, which affects the machining;
the unbalanced state of the rotating shaft results in the excessive wear of the bearings, and the overfatigue of the bearing structure; and
the unbalanced state of the rotating shaft results in power loss.
It can be seen that, whether a rotating shaft is in a balanced state or not is an important issue in machining and, therefore, it is necessary to provide a method for detecting the unbalanced state of the rotating shaft.
The unbalanced state of a rotating element can be detected, for example, by using an additional sensor, wherein the sensor detects the distance change between a rotor's actual position and a reference position, and sends out a corresponding signal when the occurrence of an unbalanced state is determined. Alternatively, a vibration or physical pressure of a system can be measured with an electric sensor, wherein an accelerometer is used to measure the vibration in the system, with a signal processing system determining a spectral power density of the measured value, thereby determining the frequency spectrum and a total energy spectrum of the measured vibration, and determining the unbalanced state of the rotor by the energy spectrum of the vibration. In another approach, a test weight can be externally applied to the rotating body and the introduced vibrations measured with a vibrating sensor.
The above-mentioned methods require expensive additional sensors or trial weights which are difficult to install in the equipment, especially in the rotary drive system of precision equipment; in addition, these measurement need to be performed by trained personnel.
In another approach that does not require an additional sensor or weight, the unbalanced state of a load is derived from signals of a motor driver, wherein a phase angle spectrum is determined from the phase angle between a stator winding voltage and a stator winding current, wherein the difference between a maximum phase angle and a minimum phase angle during a mechanical period is used as an indication when the load is in an unbalanced state. However, this approach is rather qualitative and thus cannot provide the relevant data for subsequent manual or automatic correction.
The above-mentioned various cases of poor clamping state of the workpiece will all lead to an error during machining and seriously affect the machining accuracy and precision, and therefore, it is necessary to provide a method for detecting the clamping state of a workpiece.
The currently available methods for detecting the clamping state of a workpiece generally use a micrometer gauge to perform the manual measurement, and the efficiency of such methods is low and reading errors are prone to occur.
It would therefore be desirable and advantageous to address prior art problems and to obviate other prior art shortcomings by quantitatively detecting and measuring the unbalanced state of a rotating shaft and assessing the clamping state of a workpiece.